The mechanism of substrate inhibition of tension in skeletal muscle will be correlated with the ATPase rates of skinned fibers developing steady tension. We will also determine the force velocity relation over the range of substrates that regulate tension in the absence of calcium to determine the degree of correspondence between a given steady state tension and the form of the force velocity relation. We will continue our study of the morphology of the transverse tubular system (TTS) in crayfish muscle and the correlation between change in the TTS morphology and change in its electrophysiological properties.